The present invention relates to matrix print heads and, more particularly, to an improved ballistics-type matrix print head.
Ballistic-type matrix print heads generally comprise a stylus guide assembly, a plurality of electromagnetic structures coupled to the guide assembly, each structure including an inner pole piece, an outer pole piece and a coil wrapped around the inner pole piece. A plurality of armatures are disposed radially about the guide assembly. Each armature is associated with one of the electromagnetic structures to form an electromagnetic actuator for transferring electromechanical energy to a stylus. Each of the armatures as an inner end and an outer end projecting outwardly of the associated outer pole piece. A plurality of styli are respectively associated with the plurality of armatures, each stylus being carried by the guide assembly and having an armature engaging end for engaging the inner end of the associated armature and a printing end for impacting a record medium when the stylus is propelled through the guide assembly by energization of the associated electromagnetic actuator.
Ballistics-type matrix print heads also usually include one or more armature retainers coupled to the guide assembly for retaining each armature in engagement with its associated outer pole piece. One known ballistics-type matrix print head uses an armature retainer comprised of a single unitary connector having a central portion connected to the guide assembly and a plurality of resilient arms extending axially outward from the central portion. Each of the arms engages the outer end of one of the plurality of armatures for biasing the armature into engagement with the associated outer pole piece, while at the same time applying a moment of force to the armature tending to cause the inner end thereof to rotate about the outer pole piece toward the central portion of the connector.
It is necessary to maintain engagement between the armature and its associated outer pole piece in order to maintain an appropriate magnetic path for the associated electromagnetic actuator. Further, it is desirable to bias the inner ends of the armatures upwardly toward the center portion of the connector for contact with a shock absorbing member mounted therein. Such biasing is thereby intended to effect a simultaneous mutual alignment of the armatures' inner ends so that all actuated sytli will strike a record medium at substantially the same instant of time.
The unitary connector type of armature retainer described above has led to some disadvantages and problems. For one, the biasing force tending to hold each armature engaged with its associated outer pole piece and to rotate the armature inner end upwardly relative to such outer pole piece is applied on an individual basis by the associated resilient arm of the unitary connector. Thus, since there is the possibility of distortion in some arms and general non-uniformity of structure and design among the arms as a whole due to the fabrication process, it will be apparent that there may be corresponding non-uniformity of armature travel. Such non-uniformity may, of course, result in some of the actuated styli striking the record medium at different instants of time.
Another problem with the unitary connector type of armature retainer results from the resilient nature and use of plural individual arms. It has been found that these arms tend to break off by persons either assembling the head, mounting it into a matrix printer unit, or operating such printer. More specifically, since the arms are independently movable relative to one another, they can be inadvertently bent and broken off. This is especially true when considering the fact that the armature outer ends extend outwardly of the head as a whole. They can thus get caught and moved upwardly, thereby causing the associated arm to be bent upwardly and thereby either distorted or broken.
It would be desirable, therefore, to provide a ballistics matrix print head having an improved armature retainer which is substantially free of the above-mentioned disadvantages and problems.